AIR-CONDITIONING

SYSTEM

LEARNING OUTCOME

At the end of the lecture the student will be able to:

Explain the important of Air-conditioning

Sketch and explain the process of cooling the air

Describe the function of compressor, condenser, expansion valve and evaporator

Distinguish between split unit and central unit of air-conditioning

Explain the function of AHU, Chiller and cooling tower

Show the heat transfer in air-conditioning system

INTRODUCTION

Air-conditioning is the process of cooling the air

in a building to provide a comfortable

temperature.

It is divided by two, forced air conditioning

system and hydronic (hydronic is the name for

the use of water as the heat-transfer medium in

heating and cooling systems) air conditioning

system.

Air-Conditioning

System

Forced Air

Conditioning System

Hydronic Air

Conditioning System

Air-Conditioner Chiller

Unit System/Package Unit

Central Plant System

Air Cooled Water CooledSplit Unit Window Unit

TYPES OF AN AIR CONDITIONING SYSTEM

ADVANTAGES OF AN AIR CONDITIONING SYSTEM

Improve working efficiency, reduce illness and absenteeism

(absenteeism is a habitual pattern of absence from a duty or obligation).

Increase sales, productivity and comfort ness.

Less cleaning, material and furniture last longer.

Suitable environments for plants grow process, electronic and lab areas.

Reduce internal and external pollution e.g. dust, noise and smoke

Less risk of fire or damage due to static electricity caused by dry air

FACTORS OF CHOOSING TYPES OF SYSTEM

Size – volume

Usage – people, process

Arrangement of rooms, buildings

Building materials – heat retained

Water or air for releasing heat from condenser

Noise level of system used

Reliability, installation, cost & maintenance

Flexibility or user friendly

SELF CONTAINED (LOCALISED)

SPLIT UNIT•Most central air conditioning units operate by

means of a split system because of

Low-cost

Results in reduced noise

inside the house. (at the

expense of increased noise

outside the house).

Are perfect for those that do not have central air conditioning & do not want to settle for the noise & inefficiency of window units.

Offer higher efficiency & reduced noise without a large hole in the wall/ an open window.

By separating the compressor & condenser coil from the fan & evaporator coil, the noisiest component is away from the room.

The indoor unit will usually have remote control capabilities and a timer to cycle the system only when needed. The indoor unit is called an air handler because it has the evaporator coil, blower & controls inside.

The outdoor unit is called the condenser.

They are connected together with refrigerant

piping & control wiring, similar to a central system.

Since mini splits have no ducts, they avoid the energy losses

associated with ductwork of central forced air systems.

Duct losses can account for a significant portion of energy

consumption for space conditioning, especially if the ducts are

in a unconditioned space such as an attic.

“hot” side( condensing unit): including condensing coil, compressor and fan- situated outside home.

Consists of a long, spiral coil cylinder shaped. Inside the coil – fan: blow air through the coil, along with a weather-resistant compressor and some control logic.

"cold" side : consists of an expansion valve and a cold coil, and it is usually part of your furnace or some type of air handler.

Furnace blows air through an evaporator coil, which cools the air. This cool air is routed throughout your home by means of a series of air ducts.

WINDOW UNIT

Compressor, evaporator, condenser and

expansion valve are in a compact unit at the

wall.

Suitable for individual rooms or offices with at

least one external wall.

Only disadvantages of window units are

noisy, no fine control of temperature and

humidity and higher consumption of electricity

per ton.

Ideal when only a few rooms are to be

cooled and individual controls are required.

Initial cost is low.

There are basically two types of package system – air-

cooled or water-cooled

Generally used with ductwork.

Provide better control than window units - have more

than one compressor, cylinder unloading compressors,

split coils, time delay starters, etc.

CENTRAL PLANT PACKAGE

AIR-COOLED

Consist of multi stage blower like window unit.

It is located in one big room or outside the building.

Cooling capacities and volume of air delivered by the

units would depend on individual manufacturers.

Generally for air-cooled packed units the cooling

capacities are from about 2 tons to about 20 tons (2

HP to 30 HP).

The nominal delivery volume of air delivered is about

500 cfm per ton.

Split into the compressor condenser section and the

fan coil section - provides more flexibility in

equipment placement but the distance between these

two sections should not be too much or the refrigerant

piping sizes would have to be increased.

Overall efficiency of packages units 7 to 11 btu/hr per

watt for air cooled packaged units

WATER-COOLED

Consist of AHU and blower chilled.

Consist of compressor, condenser, expansion valve

and evaporator.

For water-cooled packed units, the cooling

capacities are from about 2 tons to about 50 tons (2

HP to 60 HP)

The overall efficiency of packages units range from

9 to 15 btu/hr per watt for water cooled equipment.

Refrigeration cycle

BASIC AIR-COND SYSTEM

AN AIR CYCLE An air cycle is the process of distributing

the clean air to the particular room to be cooled. The purpose of cycle is actually removes heat from that room.

Removed heat in this cycle occurs when the return supply air are absorb at the condenser. The heat condensing medium using either air or water. So, this cycle have supply distribution and return distribution.

The method of this distributing might be using air ducting or cooling water piping.

Complete system of an air conditioner need the refrigeration cycle and air cycle. In air cycle there is a few component to be use such as:

a)Air Handling Unit

b)Air Filter

c)Air Ducting

d)Clean air inlet

e)Humidification Equipment

f)Dehumidification Equipment.

AIR-CONDITIONING COMPONENTS

1. Air Handling Unit

2. Expansion Valve

3. Condenser

4. Compressor

5. Evaporator

6. Chiller

AIR CONDITIONING

COMPONENTS

COMPRESSOR

EXPANSION

VALVE

EVAPORATOR

CONDENSER

Air Handling Unit (AHU)

AHU is function for the process of heating, cooling,

humidification, dehumidification, air filtering and air

distribution.

Therefore, it is also reprocess the return air from

particular cooled room

AIR HANDLING UNIT

Refrigerant

A refrigerant is a compound used in a heat cycle that undergoes a phase change from a gas to a liquid and back.

The two main uses of refrigerants are refrigerators/freezers and air conditioners

the most widely used refrigerants were the halomethanes R-12 and R-22, with R-12 being more common in automotive air conditioning and small refrigerators, and R-22 being used for residential and light commercial air conditioning, refrigerators, and freezers.

EXPANSION VALVE

EXPANSION VALVE

Refrigerant enters the inlet & screen as a high-pressure liquid. Refrigerant flow is restricted by a metered orifice through which it must pass.

As the refrigerant passes through this orifice, it changes from high-pressure liquid to low-pressure liquid (passes from high side to low side of the system).

Expansion valve removes pressure from the liquid refrigerant to allow expansion/change of state from a liquid to a vapor in the evaporator.

High-pressure liquid refrigerant entering the expansion valve is quite warm. The liquid refrigerant leaving the expansion valve is quite cold. The orifice within the valve does not remove heat, but only reduces pressure.

CONDENSER

Is a heat exchanger that removes heat from high

pressure refrigerant vapor. High pressure refrigerant

vapor flows through the condenser and a condensing

medium passes across the outside of the condenser.

Heat flows from the hot refrigerant vapor to the cold

condensing medium.

A condensing medium is a fluid (air or water) that has a

lower temperature than the refrigerant, which causes

heat to flow to the medium.

A condensing medium removes heat from a

refrigerant because it has a lower

temperature than the refrigerant.

Air and water condensing mediums used in

refrigeration system.

As a refrigerant vapor gives up heat to the

condensing medium in a condenser, the

vapor condenses to a liquid.

COMPRESSOR

COMPRESSOR

Purpose of the compressor is to circulate therefrigerant in the system under pressure, thisconcentrates the heat it contains.

At the compressor, the low pressure gas ischanged to high pressure gas.

This pressure build up can only beaccomplished by having a restriction in thehigh pressure side of the system. This is asmall valve located in the expansion valve.

EVAPORATOR

EVAPORATOR

Evaporator coils of air conditioning systems aresometimes called cooling coils. They are alsoused in air-handling units.

They contain chilled water. They are completelydifferent from those used in direct expansionair-cond units. So cooling coils is not anaccurate word to use in small air-cond units.Evaporator coils should be used instead.

Evaporator tubes must contain refrigerant liquidthat can evaporate to become gas. In an airconditioning system, when the liquid refrigerantabsorbs heat, it turns to gas. The heat is thustransferred to the refrigerant.

That's how the heat is moved from one locationto another location. The evaporator coils arelocated in the low-pressure system of arefrigeration circuit.

CHILLER

Unit where chilled water is cooled by the evaporator.

The chilled water is circulated inside the cooling coil in the AHU, being warmed and to the chiller.

Inside the chiller, the low pressure liquid refrigerant inside the evaporator absorbs heat and flows to the condenser.

The condenser is either air-cooled or water-cooled.

This unit is usually installed for central plant system.

AIR-CONDITIONING OPERATE

An air conditioner is able to cool a building

because it removes heat from the indoor air

and transfers it outdoors.

A chemical refrigerant in the system absorbs

the unwanted heat and pumps it through a

system of piping to the outside coil. The fan,

located in the outside unit, blows outside air

over the hot coil, transferring heat from the

refrigerant to the outdoor air.

What happen when the heat/cool the

air without adding moisture

50% 25%

10oC 20oC

Suitable heating i.e no moisture added

If the air heated from 10oC to 20oC the RH = 25% (too low)

30oC25oC

95% 70%

Suitable cooling i.e no moisture added

If the air is cooled from 30oC to 25oC the RH = 95% (too high)

Cooling of air without adding moisture/dehumidification

Human comfort level

70% 60%

5oC 20oC

Washing & cooling

preheating

Fine heating

Cooling to 9oC in the washer

Human comfort level;Temp = 20ocRelative humidity= 60% -70%

If the air enters the plant at 5oC and with a RH of 70% and the room air is required at 20oc with RH of 60% the air will require preheating to 18.5oc, cooled to 9oc dew point temperature and then finally heated to 20oC

Figure shows cooling air by preheating, washing and final heating

CASE STUDY

Location: University

Technology MARA Pulau

Pinang

Topic: Air-Conditioning

Air-Conditioning Location: Kolej

Baiduri and Zamrud

Type of Air-Conditioning: Ceiling

exposed split type

Name of brand: Fujitsu (Japan)

Location: University Technology MARA Pulau Pinang

Topic: Air-Conditioning

Air-Conditioning Location: Laman Perdana

Type of Air-Conditioning: Floor Standing Split type

Name of brand: Yonan (China)

Dimensions for indoor units: 600 x 350 x 1900mm

Net weight for indoor units: 55kg

Cooling capacity:42000btu

Heating capacity: 45000btu

Voltage: 220V/50Hz, 240V/60Hz

Location: Pangsapuri Idaman

Topic: Air-Conditioning

Air-Conditioning Location: House

Type of Air-Conditioning: Wall mounted

split type

Name of brand: Toshiba (Japan)

Dimensions for indoor units: 1070 x 295 x 370mm

Dimensions for outdoor units: 850 x 290 x 610mm

Net weight for indoor units: 14kg

Net weight for outdoor units: 47kg

Cooling capacity: 22000btu

Heating capacity: 22000btu

Voltage: 220V/50Hz, 240V/60Hz

CONDENSER

The condenser is a heat

exchanger that removes

heat from high pressure

refrigerant vapor.

As the refrigerant passes

through the condenser

coil and the cooler

outside air passes across

the coil, the air absorbs

heat from the refrigerant,

which causes the

refrigerant to condense

from a gas to a liquid

state.

The high-pressure, high-temperature liquid then reaches the expansion valve.

EXPANSION VALVE

The expansion valve is the "brain" of the system.

By sensing the temperature of the evaporator, or

cooling coil, it allows liquid to pass through a very

small orifice, which causes the refrigerant to expand to

a low-pressure, low-temperature gas.

This "cold" refrigerant flows to the evaporator.

EVAPORATOR

• is a heat exchanger that adds

heat to low pressure refrigerants liquid flows through the evaporator an evaporating medium passes across the outside of the evaporator.

• An evaporating medium is a fluid that is cooled when heat is transferred from medium to the cold refrigerant.

•An evaporating medium adds heat to a refrigerant because it has a higher temperature than refrigerant.

•As the liquid refrigerant absorb heat from the evaporating medium the refrigerant boils and vaporizes.

COMPRESSOR

-The compressor is the "heart" of the system.

-It acts as the pump, causing the refrigerant to flow through the system.

- Its job is to draw in a low-pressure, low-temperature, refrigerant in a gaseous state and by compressing this gas, raise the pressure and temperature of the refrigerant.

- This high-pressure, high-temperature gas then flows to the condenser coil.

Pump

AIR HANDLING UNIT (AHU)

The AHU is box-like equipment with a fan and a

cooling coil inside. Some units also contain air

filters. The whole fan and motor assembly,

comprising shaft, bearings, pulley, belting is usually

put inside the AHU.

to suck air from the rooms, let it pass through

chilled water cooling coils and then discharging the

cooled air back to the rooms.

A certain amount of fresh air may be introduced at

the suction duct so that air in the rooms may be

gradually replaced.

The cold air is transfer to the

next room.

If humidity of the air has to be controlled, steam coils, or other heating coils may be installed

Moisture in the air is condensed out when it comes into contact with the chilled water coils. At the bottom of the AHU, a pipe is installed so that water that is collected can be drained out.

Removable panels are installed so that personnel can enter into the AHU for maintenance. Maintenance is mostly changing or washing of air filters, greasing of bearings, changing of belts, and general inspection and cleaning work.

Fan (tangential type) of the

air handling unit

Hole of the flow of the fresh

air

CHILLED WATER SYSTEM

Chiller - heart of the central air conditioning system.

Better - To cool down a large building.

Chilled water is easily pumped and it is able to reach all floors in the building.

Chillers make use of the refrigeration

principles to work.

The flow of the heat in central air conditioning system:

• Heat is transferred from the air in the rooms to chilled

water at the air handling units.

• The chilled water is pumped through the chiller and the

heat is transferred to the refrigerant.

• The refrigerant is cooled by cooling water circulating in the

condenser of the chiller.

• The heated cooling water is passed through cooling towers

where the heat is dissipated to the atmosphere by fans.

A pipe connecting the compressor to cooling tower. CWP at the pipe bring means cooling water.

A pipe connecting the compressor to AHU room. CHW at the pipe means chilled water.

COOLING TOWER

used in central air conditioning systems.

function - to cool the warm water from the chiller

condenser.

heat from the rooms in a building is transferred

to chilled water, then transferred into the

refrigerant, and finally to the cooling water. The

cooling tower is at the final point of the heat

transfer. The heat is transferred to the

atmosphere.

heat in the cooling water is removed

by letting moving air come into

contact with it.

Water is normally spread out and

allowed to drop down by gravity from

a height.

Plastic fillings are arranged so as to

increase the wetted surface of the

water while it is dropping, while at the

same time provide better contact

between the air passages and the

water.

Cooling Tower

Big fan for cooling tower

CONCLUSION

The design objective of air-conditioning system is to control

indoor parameters within required thermal comfort and indoor

air quality overall. The air conditioning system is the one most

important devices to give the fresh air especially in house and

room.